Nostalgia is a sentimentality for the past, typically for a period or place with happy personal associations. The word nostalgia is learned formation of a Greek compound, consisting of νόστος (nóstos), meaning "homecoming", a Homeric word, and ἄλγος (álgos), meaning "pain, ache", and was coined by a 17th-century medical student to describe the anxieties displayed by Swiss mercenaries fighting away from home. Described as a medical condition—a form of melancholy—in the Early Modern period, it became an important trope in Romanticism.

Nostalgia can refer to a general interest in the past, its personalities, and events, especially the "good old days" from earlier in one's life.

The scientific literature on nostalgia usually refers to nostalgia regarding the personal life and has mainly studied the effects of nostalgia induced during the studies. Smell and touch are strong evokers of nostalgia due to the processing of these stimuli first passing through the amygdala, the emotional seat of the brain. These recollections of one's past are usually important events, people one cares about, and places where one has spent time. Music[ and weather can also be strong triggers of nostalgia. Nostalgic preferences, the belief that the past was better than is the present, has been linked to biases in memory.

Although nostalgia is often triggered by negative feelings, it results in increasing one's mood and heightening positive emotions, which can stem from feelings of warmth or coping resulting from nostalgic reflections. One way to improve mood is to effectively cope with problems that hinder one's happiness. Batcho (2013) found that nostalgia proneness positively related to successful methods of coping throughout all stages—planning and implementing strategies, and reframing the issue positively. These studies led to the conclusion that the coping strategies that are likely among nostalgia prone people often lead to benefits during stressful times. Nostalgia can be connected to more focus on coping strategies and implementing. them, thus increasing support in challenging times.